Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), and synchronous dynamic random access memory (SDRAM).
DRAM arrays are manufactured by replicating millions of identical circuit elements, known as DRAM cells, on a single semiconductor wafer. A DRAM cell is an addressable location that can store one bit (binary digit) of data. In its most common form, a DRAM cell consists of two circuit components: a storage capacitor and an access field effect transistor. The capacitor holds the value of each cell, namely a “1” or a “0,” as a charge on the capacitor. Because the charge on a capacitor gradually leaks away, DRAM capacitors must be refreshed on a regular basis. A memory device incorporating a DRAM memory includes logic to refresh (recharge) the capacitors of the cells periodically or the information will be lost. Reading the stored data in a cell and then writing the data back into the cell at a predefined voltage level refreshes a cell.
The DRAM device also includes additional components. These components include anti-fuses that can be used for a variety of applications including storing operation data or selectively enabling or disabling components on a DRAM circuit. For example, an anti-fuse can enable redundant rows of memory cells that are used to replace defective rows of memory cells, thereby allowing an otherwise defective memory to be utilized.
An anti-fuse is a programmable link that has been developed for use in integrated circuit applications. Instead of the programming mechanism causing an open circuit, as in the case with fusible links, the programming mechanism in an anti-fuse circuit creates a short circuit or relatively low resistance link. The anti-fuse link thus presents an open circuit prior to programming and a low resistance connection after programming. Anti-fuse links consist of two electrodes comprised of conductive and/or semiconductive materials and having some kind of a dielectric or insulating material between them. During programming, the dielectric in between the conductive materials is broken down by predetermined applied voltages, thereby electrically connecting the conducting and/or semiconducting materials together.
As the performance of electronic devices increases, the performance of the DRAM used in the system needs to increase as well. One method used to increase DRAM speed and density is to shrink the size of the memory array and other components in order to fit more on a single die.
One problem with shrinking the components of a DRAM is that the anti-fuses cannot easily be reduced in size. These components and their peripheral circuitry, such as power buses, remain relatively large and require a substantial amount of current to program. Gate oxide anti-fuses have been used to replace the standard anti-fuse but they can have problems with being reliably programmed.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for scalable anti-fuses.